FIG. 6 is a block diagram showing a conventional power saving structure for the wireless LAN device disclosed in Japanese unexamined patent application 8-307428 (Tokukaihei 8-307428/1996; published on 22 Nov. 1996). A receiver section 202 in the conventional wireless LAN device 201 includes: a radio section 225 which makes up the analog section; and a reception strength determine section 226, a power/clock control section 227, an A/D converter section 228, a despreader/demodulator section 229, an amplitude sensor section 230, a synchronization integrator section 231, a synchronization detector section 232, and an information demodulator section 233 which make up a digital section.
The radio section 225 operates in the analog domain. The section 225 produces an intermediate frequency from an RF (radio frequency) signal received by an antenna 224 with an internal amplifier and filter, to obtain a necessary reception strength. The reception strength determine section 226 amplifies, rectifies, and smoothes the intermediate frequency signal and compares the resultant signal strength to a predetermined value with an internal comparator to determine whether to start reception. The power/clock control section 227 controls power and clock supply to each block. The A/D converter section 228 converts the output of the radio section 225 from analog to digital. The despreader/demodulator section 229 demodulates a spread signal by despreading. The amplitude sensor section 230 produces a value indicating the amplitude of the output of the despreader/demodulator section 229. The synchronization integrator section 231 integrates the output of the amplitude sensor section 230 for each symbol. The synchronization detector section 232 produces a synchronization signal from the output of the synchronization integrator section 231. The information demodulator section 233 demodulates for information based on the output of the amplitude sensor section 230 and the synchronization signal output of the synchronization detector section 232.
Now, the receiver section 202 in the wireless LAN device 201 will be described in terms of its operation.
In reception standby periods, only the radio section 225 (analog section), the reception strength determine section 226, and the power/clock control section 227 are in operation. The power/clock control section 227, in the reception standby period, is suspending operation clock supply to the A/D converter section 228, the despreader/demodulator section 229, the amplitude sensor section 230, the synchronization integrator section 231, the synchronization detector section 232, and the information demodulator section 233 which therefore are not operating.
In these circumstances, the reception strength determine section 226 amplifies the intermediate frequency signal from the radio section 225 and compares the strength of the intermediate frequency signal to a value specified by the terminal device with an internal comparator. If the strength of the intermediate frequency signal is greater, reception is started.
Following the start of reception, the power/clock control section 227 supplies an operation clock to the A/D converter section 228, the despreader/demodulator section 229, the amplitude sensor section 230, the synchronization integrator section 231, the synchronization detector section 232, and the information demodulator section 233 to place them in operation.
After a termination of reception, only the radio section 225 (analog section), the reception strength determine section 226, and the power/clock control section 227 are again in operation.
The structure lowers power consumption in the wireless LAN device which stands by for an extended period of time for reception.
However, in this conventional structure, in reception standby periods when the digital section (A/D converter section 228, despreader/demodulator section 229, amplitude sensor section 230, synchronization integrator section 231, synchronization detector section 232, and information demodulator section 233) is not operating, the radio section 225 (analog section) is in operation. The radio section 225 includes various analog circuits which, when combined, consume quite a lot of operating power. This waste of power cannot be ignored, especially, when the wireless LAN device is mounted to a mobile terminal.